This application requests funds for a new, high performance gas-chromatograph-mass spectrometer to be used as a shared facility in the Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, Rockefeller University. This laboratory has provided mass spectrometric service for Rockefeller University and its neighboring biomedical institutions and for the metropolitan New York biomedical community. The new instrument is needed to replace our absolescent DuPont 21-492 mass spectrometer. The major specific capabilities required are: high sensitivity, rapid scanning for capillary GCMS service, multiple ion detection for quantitation, high resolution for atomic composition determination, and ability to produce and measure both positive and negative ions. The instrument which best meets these requirements and therefore is the one desired is the VG MM7070E.